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Message-Id: <1256813310.7574.3.camel@marge.simson.net>
Date: Thu, 29 Oct 2009 11:48:30 +0100
From: Mike Galbraith <efault@....de>
To: Ingo Molnar <mingo@...e.hu>
Cc: Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
hpa@...or.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de
Subject: Re: [patch] Re: [regression bisect -next] BUG: using
smp_processor_id() in preemptible [00000000] code: rmmod
On Thu, 2009-10-29 at 10:19 +0100, Mike Galbraith wrote:
> On Thu, 2009-10-29 at 10:14 +0100, Ingo Molnar wrote:
>
> > hm, the problem is kthread_bind(). It is rummaging around in scheduler
> > internals without holding the runqueue lock - and this now got exposed.
> > Even though it is operating on (supposedly ...) inactive tasks, the guts
> > of that function should be moved into sched.c and it should be fixed to
> > have proper locking.
>
> Yeah, I was thinking that nobody should ever be able to hit that without
> it being a bug.. but wimped out.
How about so?
sched: Move the body of kthread_bind() to sched.c.
Eric Paris reported that commit f685ceacab07d3f6c236f04803e2f2f0dbcc5afb
causes boot time PREEMPT_DEBUG complaints.
[ 4.590699] BUG: using smp_processor_id() in preemptible [00000000] code: rmmod/1314
[ 4.593043] caller is task_hot+0x86/0xd0
[ 4.593872] Pid: 1314, comm: rmmod Tainted: G W 2.6.32-rc3-fanotify #127
[ 4.595443] Call Trace:
[ 4.596177] [<ffffffff812ad35b>] debug_smp_processor_id+0x11b/0x120
[ 4.597337] [<ffffffff81051d66>] task_hot+0x86/0xd0
[ 4.598320] [<ffffffff81066275>] set_task_cpu+0x115/0x270
[ 4.599368] [<ffffffff810985ab>] kthread_bind+0x6b/0x100
[ 4.600354] [<ffffffff810914f0>] start_workqueue_thread+0x30/0x60
[ 4.601545] [<ffffffff810941dd>] __create_workqueue_key+0x18d/0x2f0
[ 4.602526] [<ffffffff810d9bee>] stop_machine_create+0x4e/0xd0
[ 4.603811] [<ffffffff810c5818>] sys_delete_module+0x98/0x250
[ 4.604922] [<ffffffff810e2505>] ? audit_syscall_entry+0x205/0x290
[ 4.606202] [<ffffffff81013202>] system_call_fastpath+0x16/0x1b
Since kthread_bind() messes with scheduler internals, move the body to sched.c,
and lock the runqueue.
Signed-off-by: Mike Galbraith <efault@....de>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Reported-by: Eric Paris <eparis@...hat.com>
LKML-Reference: <new-submission>
---
kernel/kthread.c | 15 ++++++---------
kernel/sched.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 37 insertions(+), 9 deletions(-)
Index: linux-2.6/kernel/kthread.c
===================================================================
--- linux-2.6.orig/kernel/kthread.c
+++ linux-2.6/kernel/kthread.c
@@ -149,6 +149,8 @@ struct task_struct *kthread_create(int (
}
EXPORT_SYMBOL(kthread_create);
+extern void sched_kthread_bind(struct task_struct *k, unsigned int cpu);
+
/**
* kthread_bind - bind a just-created kthread to a cpu.
* @k: thread created by kthread_create().
@@ -157,18 +159,13 @@ EXPORT_SYMBOL(kthread_create);
* Description: This function is equivalent to set_cpus_allowed(),
* except that @cpu doesn't need to be online, and the thread must be
* stopped (i.e., just returned from kthread_create()).
+ *
+ * The runqueue must be locked, ergo move the body if this function
+ * to sched.c
*/
void kthread_bind(struct task_struct *k, unsigned int cpu)
{
- /* Must have done schedule() in kthread() before we set_task_cpu */
- if (!wait_task_inactive(k, TASK_UNINTERRUPTIBLE)) {
- WARN_ON(1);
- return;
- }
- set_task_cpu(k, cpu);
- k->cpus_allowed = cpumask_of_cpu(cpu);
- k->rt.nr_cpus_allowed = 1;
- k->flags |= PF_THREAD_BOUND;
+ sched_kthread_bind(k, cpu);
}
EXPORT_SYMBOL(kthread_bind);
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2063,6 +2063,37 @@ void set_task_cpu(struct task_struct *p,
__set_task_cpu(p, new_cpu);
}
+/**
+ * sched_kthread_bind - bind a just-created kthread to a cpu.
+ * @k: thread created by kthread_create().
+ * @cpu: cpu (might not be online, must be possible) for @k to run on.
+ *
+ * Description: This function is equivalent to set_cpus_allowed(),
+ * except that @cpu doesn't need to be online, and the thread must be
+ * stopped (i.e., just returned from kthread_create()).
+ *
+ * Function lives here instead of kthread.c because it messes with
+ * scheduler internals which require locking.
+ */
+void sched_kthread_bind(struct task_struct *p, unsigned int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+ unsigned long flags;
+
+ /* Must have done schedule() in kthread() before we set_task_cpu */
+ if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
+ WARN_ON(1);
+ return;
+ }
+
+ spin_lock_irqsave(&rq->lock, flags);
+ set_task_cpu(p, cpu);
+ p->cpus_allowed = cpumask_of_cpu(cpu);
+ p->rt.nr_cpus_allowed = 1;
+ p->flags |= PF_THREAD_BOUND;
+ spin_unlock_irqrestore(&rq->lock, flags);
+}
+
struct migration_req {
struct list_head list;
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